1. Field of the Invention
The present invention relates to a communication device and a communication control method for carrying out communications according to a control protocol such as Echonet on a network using a network layer protocol such as IP (Internet Protocol).
2. Description of the Related Art
In recent years, the information home electronics have been developing rapidly. This field encompasses a wide variety of devices such as home appliances, AV home electronics, information devices or mobile devices such as PCs, etc., and various applications utilizing the digital technology have been proposed for each device.
One such application is the use of a home network. The home network is a network technology developed for a network inside the home, for interconnecting various information home electronics mentioned above.
As this home network technology, the Internet technology has been attracting much attentions recently. For example, many applications that are attractive to the home network users such as those of music distribution, home page viewing, e-mails, etc., have been developed and the number of users is steadily increasing.
On the other hand, one exemplary application of the home network is a facility related network, or the use of the home network for the home automation. It is possible to connect air conditioners, lights, home appliances, etc., to the home network and carry out applications such as device state monitoring, remote controlling, etc.
In Japan, the Echonet is expected to be the de facto standard for this facility related network. The Echonet defines commands, protocols, objects, API, etc. for controlling facility related devices (home appliances, etc.) on various physical media such as electric power lines, twisted pair lines, etc. Further details of the Echonet can be found in documents disclosed at the URL “http://www.echonet.gr.jp”, for example. The Echonet is standardized by a consortium founded mainly by several Japanese electronics companies, which has already issued the specification version 1, and the commercial application is about to start.
The Echonet has its own address system, so that there is a need for a mechanism to use the address system of the Echonet on the address system of the Internet. To this end, it is necessary to account for things that have not been accounted so far, such as the determination of a correspondence relationship between the Echonet address and the Internet address. This is done by the Echonet address initialization procedure.
In the case of determining the Echonet address, it can be expected that an Echonet address server for determining the Echonet address may not necessarily exist, so that there is a need to provide a mechanism for determining the Echonet address independently. An example of such a mechanism is that in which “a candidate value for the Echonet address is selected and broadcasted on the local network to check the address overlap”. In this mechanism, there is a possibility for a loop of “selecting a tentative address value→checking→discovering overlap→going back to start” to take some time. For this reason, there can be cases where the own Echonet address cannot be determined during some period of time after the activation.
In particular, in the case of implementing this mechanism on the radio scheme such as Bluetooth, because the Bluetooth has a limitation that the number of nodes (the number of slaves) that can actively carry out communications simultaneously is limited to be less than or equal to seven, there is a possibility for the above loop to require much time, especially in view of the fact that the above loop utilizes the broadcast processing.